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https://github.com/luvisi/continuinglogo

A Logo interpreter with dynamic scope, shallow binding, tail call optimization, Lisp 1.5 style FUNARG's, and first class continuations. Mostly Ucblogo compatible.
https://github.com/luvisi/continuinglogo

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A Logo interpreter with dynamic scope, shallow binding, tail call optimization, Lisp 1.5 style FUNARG's, and first class continuations. Mostly Ucblogo compatible.

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ContinuingLogo



ContinuingLogo is a Logo interpreter that is mostly compatible with

Ucblogo.  It successfully runs minimally modified versions of 

Brian Harvey's Pascal compiler and Student program from volume 3 of

Computer Science Logo Style.



It also supports FUNARG's, which are kind of like lexical closures,

but they are closed over the dynamic environment instead of the

lexical environment.  These were in Lisp 1.5, but they have not

been implemented in many recent languages.



For example:



    ? to addx :y

    >   output :x+:y

    > end

    ? to makeclosure

    >   output function [[z] addx :z]

    > end

    ? to makeadder :x

    >   output makeclosure

    > end

    ? make "add5 makeadder 5

    ? print invoke :add5 2

    7

    ?



When makeclosure calls function, it captures the dynamic environment,

including the value of x from makeadder.



First class continuations are supported, as is McCarthy's ambiguous

operator.  For example:



    ? to foo

    >   localmake "x (amb 1 2 3)

    >   localmake "y (amb 4 5 6)

    >   if :x*:y <> 15 [fail]

    >   print :x

    >   print :y

    > end

    ? foo

    3

    5

    ?



The garbage collector is precise, tracing, incremental, and portable.

It knows nothing about the structure of Logo objects.  Callbacks

are used for following the pointers within objects.



INSTALLATION



ContinuingLogo uses autoconf.  With any luck, the following may work:



    $ ./configure; make; make install



RUNNING



Normal usage:



    $ clogo



EXAMPLES



To run the pascal compiler:



    $ cd ucblogo/

    $ rlwrap clogo

    ? load "pascal

    Loaded

    ? compile "tower

    

    ? prun "tower

    



To run the student example:



    $ cd ucblogo/

    $ rlwrap clogo

    ? load "student

    Loaded

    ? student :radio

    



LICENSE



Most of the interpreter is released under version 3 or later of the GNU

General Public License.



The Logo library procedures in ucblogolib.txt are from Ucblogo and

are covered by version 2 or later of the GNU General Public License.



The garbage collector is released under version 2.0 of the Apache

License.



LIMITATIONS AND INCOMPATIBILITIES COMPARED TO UCBLOGO



* The reader and the treeifier use recursive descent parsers written in

  C.  They can be crashed with pathologically long or deep structures.



* There is no support for getter/setter notation, or GLOBAL.



* No TEST/IFTRUE/IFFALSE.



* No TAG/GOTO.



* Slot number variables only go up to ?10.



* There is no RUNPARSE.  Lists are only parsed once.  [a+b] is a list with

  three items.



* Backslashed characters do not keep any special properties.  There is no

  BACKSLASHEDP.



* SETITEM behaves the same as .SETITEM behaves.  It does not check for cycles.



* LOCAL will not work inside of templates run with APPLY, INVOKE, FOR, etc.



* There is no PENREVERSE.



* There is no PALETTE/SETPALETTE.  Color commands take rgb lists, with

  each value ranging from 0-255.



* There is no SETPENPATTERN/PENPATTERN.  (These are NOPs on several ucblogo

  platforms as well.)



* There is no SETSCRUNCH/SCRUNCH.



* SAVEPICT/LOADPICT use PNG format.  There is no EPSPICT.